1. Field of the Invention
The present invention relates to a transparent touch panel used for operating various electronic apparatuses.
2. Background Art
Recently, as electronic apparatuses have become more functional and diversified, the production of an electronic apparatus having a transparent touch panel mounted on a front surface of its display device such as a liquid crystal device has been increased. A character, sign, pattern, letter or the like which is shown on the display device is visually identified and selected using the transparent touch panel, and functions of the electronic apparatus are switched by operation of the transparent touch panel.
The conventional transparent touch panel mentioned above is described hereinafter with reference to FIG. 2. The conventional transparent touch panel has a light transmitting sheet 7. The light transmitting sheet 7 has a light transmitting upper film 1 such as polyethylene terephthalate or polycarbonate, a light transmitting lower film 2 and an acrylic adhesive layer 3 for sticking the upper film 1 to the lower film 2. An undercoat layer 4 is formed on a lower surface of lower film 2, and an upper electrical conductive layer 5 such as indium oxide tin or tin oxide is formed on undercoat layer 4 using a vacuum sputtering method or the like. Hard coat layer 6 is formed on an upper surface of upper film 1.
An undercoat layer 9 and a lower electrical conductive layer 10 are formed on an the upper surface of a light transmitting substrate 8, such as a polyethylene terephthalate film, glass, or acrylic, in the same way as lower film 2. A plurality of dot spacers 11 are formed on an upper surface of conductive layer 10 at predetermined intervals for keeping a certain space from conductive layer 5, and dot spacers 11 are made of insulating resin such as epoxy resin or silicone resin.
Then, sheet 7 and substrate 8 are stuck to each other at their outer peripheries using frame shaped spacer 12 to which adhesive is applied on an upper surface and a lower surface. Therefore, conductive layer 5 confronts conductive layer 10 with a predetermined space therebetween. Thus, the transparent touch panel is constructed.
In the transparent touch panel discussed above, upper lead electrodes (not shown) are formed on both sides of conductive layer 5, and lower lead electrodes (not shown) are formed on both sides of conductive layer 10 in an orthogonal direction with respect to the upper lead electrodes. Upper and lower lead electrodes are coupled with a detector (not shown) of the electronic apparatus via a connector for coupling. When an upper surface of sheet 7 is pressed with a finger, a pen or the like, sheet 7 is bent, so that upper electrical conductive layer 5 contacts the lower electrical conductive layer 10 at the pressed point.
The pressed point is detected by a resistance ratio between the upper lead electrode and the lower lead electrode using the detector, so that functions of the electronic apparatus are switched.
However, in the conventional transparent touch panel discussed above, when a certain point of the upper surface of sheet 7 is continuously pressed by a strong force through the finger or the operational pen, gel type adhesive layer 3 is pressed and moves toward a circumference of the pressed point. Thus, a thickness at the pressed point becomes thin. As a result, a dent tends to remain on an upper surface of upper film 1 even when the pen is removed, or upper electrical conductive layer 5 at the pressed point tends to be damaged.